Pedicle screw with vertical adjustment

ABSTRACT

An apparatus for rigid fixation of individual vertebra to the stabilizing rod. It consists of an anchor secured to the vertebra and a connector with multiple degrees of freedom linking each anchor to a rod. Pressure from the rod against a connector engages internal constricting mechanism and eliminates movement within the connection. This results in rigid fixation between individual anchors and the rod.

FIELD OF INVENTION

This invention relates to a spinal fixation device. More specifically,the present invention relates to an implant bridging together two ormore vertebra by anchoring to the posterior vertebral arch and pedicles.

BACKGROUND

Spinal fusion is utilized to correct painful movement across degeneratedor unstable spinal segment and is supplemented by fixation with screws.Screws are commonly placed through the posterior vertebral arch.Multiple fixation targets have been used in the past including facets,spinal processes, lamina, transverse processes, lateral masses andpedicles. Currently fixation through the pedicles offers the most robustpurchase and is utilized when possible.

Screws are implanted from the back to the front of the vertebra with onescrew inserted per each side per vertebra. Individual screws have to berigidly linked to eliminate movement between corresponding vertebras.(U.S. Pat. No. 5,474,555 Puno et al.). Anatomy of individual patientmakes it difficult and often impossible to line up pedicle screws in oneplane. Screws project with variable medial-lateral displacements anddifferent angulations. This places significant challenges on themechanical design of the linking system. These complex mechanisms withmultiple joints have to be manipulated in a deep wound restricted bymuscle and soft tissue.

Most of the available systems can be broken into one of three groups:plating system (U.S. Pat. No. 4,611,581); top loading rod system (U.S.Pat. No. 4,805,602, U.S. Pat. No. 5,360,431) and side loading rod system(U.S. Pat. No. 5,261,909).

The top loading rod systems utilizes a seat for the rod that projectsalong the screw trajectory and forms a ball and socket joint with thespherical screw head. It offers several degrees of freedom about thescrew axis: (i) 30-40 degrees of angular deflection from the screw axis(ii) 360 degrees of rotation about the screw axis. Any furtheradjustments have to be gained by contouring the rod to fit into the rodreceptacle of the seat. These systems offer advantages when the exposureis directly over the screw such as in muscle splitting or minimallyinvasive approaches.

In a standard midline approach screws project out into the soft tissueat the lateral extreme of the exposure. Top loaded systems requiremanipulation at this lateral extreme and side loading rod system canoffer advantages in these circumstances. In side loading rod systemsconnectors run perpendicular to the screw trajectory and the rod isplaced on the side of the screw toward the center of exposure U.S. Pat.No. 5,261,909).

SUMMARY OF THE INVENTION

The claimed invention offers a number of significant advantages overexisting art.

-   -   1. Screw-rod articulation functions as a rotating and pivoting        joint and not a ball and socket joint characteristic of top        loading systems. It allows much greater angular deflection (over        90 degrees) while still matching full 360 degree rotation.    -   2. Clamping mechanism allows substantial vertical travel along        the screw trajectory contributing to additional degrees of        freedom. This adds substantial flexibility particularly when        more then 3 screws need to be connected.    -   3. Connector can be snapped onto the screw head after screw is        placed into the bone. This keeps hardware profile minimal and        improves exposure for delivery of graft material. It also allows        for all the connectors and rods to be assembled outside of the        wound. This is particularly valuable in small direct exposures        characteristic of the minimally invasive approach.    -   4. This system can be utilized both as a top loading and side        loading system which can not be matched by the currently        available art.

In accordance with an embodiment of the present invention, there isprovided device for fixation of at least one spinal segment comprising arod, at least two bone screws and at least two connectors saidconnectors having a rod receiver, screw clamp, compression spacer and atightening nut. The rod receiver has at one end a channel with threadedwalls accepting the rod and the tightening nut, with the opposite endsliding over the screw clamp. The screw clamp has the articulating endopposite to the sliding portion and fitting over the bone screw saidbone screw having a threaded portion imbedded into the bone withprotruding articulating portion coupled with the screw clamp andallowing for a pivoting and rotational motion in uncompressed state butimmobilized by compression from the compression spacer. The compressionspacer is housed within rod receiver, engaged by the rod pressed intothe rod receiver and clamping on the screw clamp which in turn clamps onarticulation between screw clamp and bone screw

DETAILED DESCRIPTION

In its preferred embodiment device consists of a screw, screw clamp, rodreceiver, compression spacer, rod and nut (FIG. 1).

Screw has a long threaded portion placed into the bone and a protrudingcylindrical shaft with a spherical head (FIG. 2). A compressiblecylindrically shaped screw clamp of substantial thickness (FIG. 3) has aspherical cut-out at one end such that it fits precisely over the screwhead (FIG. 4). It pivots about the screw head with angle of deflectiongreater then ninety degrees and 360 degrees of revolution through theentire range of deflection.

Screw clamp (FIG. 6) tightly fits into cylindrical assembly consistingof the rod receiver and compression spacer (FIG. 7). Rod receiver has atravel tube with a tapered end which fits over the screw clamp. Theother end forms the seat for the rod bounded by threaded walls (FIG. 8).Up and down movement of the screw clamp within the rod receiver allowsfor a vertical adjustment. Compression clamp is a deformable componentfitting within the travel tube of the rod receiver (FIG. 5). It has acontact dome extending into the seat of the rod receiver. Pressure fromthe rod locked into the seat by a threaded nut, displaces thecompression spacer into the tapered end of the travel tube. Theresulting deformation of the compression spacer transfers compressiveforce onto the screw clamp. This fixes the screw head within the screwclamp and prevents any travel of the screw clamp within the travel tube.This process is repeated for each screw in the assembly.

Alternative embodiments of the screw shaft and screw clamp articulationwhich enable pivoting and rotational motion are possible.

(FIG. 13, FIG. 14).

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 Preferred embodiment of the invention showing screw (1), screwclamp (6), compression spacer (9), rod (17) and nut (18)

FIG. 1 a Different orientation of the preferred embodiment of theinvention showing screw (1), screw clamp (6), compression spacer (9),rod (17) and nut (18).

FIG. 2 Bone screw consisting of threaded portion (2), protruding shaft(3) and spherical head (4). Please notice the channel (5) through thecenter of the screw.

FIG. 3 Preferred embodiment of the screw clamp consisting of acylindrical compressible shaft (8) and articulating end (7).

FIG. 4 Articulation between screw head (4) and articulating end (7) ofthe screw clamp. Notice that this articulation allows only pivotingmotion and is not a ball-socket joint.

FIG. 5 One of the embodiments of the compression spacer (9) with contactdome (10) which is depressed by the rod (17) when its locked, andconstricting tube (11) deformed by the tapered section of the rodreceiver (16).

FIG. 6 Preferred embodiment of the rod receiver (12) consisting of theseat (13) for the rod, threaded extensions (14) which accept a nut (18),travel tube (15) and tapered end (16).

FIG. 7 Assembly consists of screw clamp (6), compression spacer (9) androd receiver (12).

FIG. 8 Preferred embodiment of the invention with compression spacer (9)and rod receiver (12) rendered transparent to demonstrate the entireassembly.

Also note the screw clamp (6) and the screw (1). Note that if deformablecompression spacer (9) is pressed into the rod receiver (12) the taperedconfiguration at the bottom of the rod receiver will constrictcorresponding area of the compression spacer, which in turn willtransmit compressive forces to the articulation between screw clamp (6)and a screw (1).

FIG. 9 (Landscape orientation)

Demonstrates 90 degrees deflection angle (potentially >90 degrees)between screw (1) and screw clamp (6).

FIG. 10 Assembly demonstrates vertical travel of screw clamp (6) withinthe rod receiver (12). Please compare to Pic 8. Please note thatcompression by compression spacer (9) will be transferred to screw clamp(6) over a wide range of vertical travel.

FIG. 11 Bone screw (1) with central channel (5).

FIG. 12. Bone screw (1) with off-center channel (5).

FIG. 13 Alternative embodiment of the screw (1) and screw clamp (6)articulation with compressible spherical spacer (19) threaded over thecylindrical screw shaft(3).

FIG. 14 Alternative embodiment of the screw (1) and screw clamparticulation. Screw clamp would be modified to fit over the projections(20) of the compressible T-spacer (21).

1. A device for fixation of at least one spinal segment comprising of arod, at least two bone screws and at least two connectors saidconnectors having rod receiver, screw clamp, compression spacer and atightening nut said rod receiver having at one end a channel withthreaded walls accepting the rod and the tightening nut; with theopposite end sliding over the screw clamp, said screw clamp having thearticulating end opposite to the sliding portion and fitting over thebone screw said bone screw having a threaded portion imbedded into thebone with protruding articulating portion coupled with the screw clampand allowing for a pivoting and rotational motion in uncompressed statebut immobilized by compression from the compression spacer saidcompression spacer housed within rod receiver, engaged by the rodpressed into the rod receiver and clamping on the screw clamp which inturn clamps on articulation between screw clamp and bone screw. 2.Device as claimed in claim 1 wherein two such devices are utilized, oneon each side.
 3. Device as claimed in claim 2 wherein two such devicesare linked by a transverse bridging member
 4. Articulating end of thebone screw as claimed in claim 1 possessing a substantially sphericalshape.
 5. Articulating end of the bone screw as claimed in claim 1possessing a cylindrical shape.
 6. Bone screw as claimed in claim 1 witha channel through its central axis
 7. Bone screw as claimed in claim 1with off-center channel entering through the tip of the screw andexiting through the side of the screw
 8. Bone screw as claimed in claim1 possessing surface protrusions and surface indentations providingmeans of handling of said screw during insertion into the bone.
 9. Rodreceiver as claimed in claim 1 with walls of the threaded channel forthe rod placement possessing substantial extensions projecting above theskin surface
 10. Extensions as claimed in claim 9 and means of removalof said extensions from the rod receiver.
 11. Rod as claimed in claim 1wherein such rod possesses protrusions or indentations at both ends ofsaid rod and means of handling such rod utilizing said protrusions orindentations.
 12. Device as claimed in claim 1 wherein the bone screwsis substituted by another bone anchoring device including but notlimited to lamina hook, transverse process hook, facet screw or facetbolt.
 13. Articulating end of the bone screw as claimed in claim 4 withuneven or knurled surface.
 14. Articulating end of the bone screw asclaimed in claim 4 with smooth surface.
 15. Articulating end of thescrew clamp as claimed in claim 1 with smooth surface.
 16. Articulatingend of the screw clamp as claimed in claim 1 with uneven or knurledsurface.